1. Field of the Invention
The present invention relates to an electromagnetic induction heater device. In particular, the present invention relates to a dual half-bridge type induction cooking apparatus for multi-output control which can minimize the construction of a circuit by constructing an inverter circuit having a plurality of inverter-modules and can remove interference noise generated when a plurality of heating plates are heated.
2. Description of the Prior Art
In a conventional induction cooking apparatus, a plurality of inverter circuits are coupled in parallel to an input power to operate a plurality of working coils.
Specifically, the conventional induction cooking apparatus, as shown in FIG. 1, includes a power supply section 1. The apparatus also includes a plurality of rectifying sections 2 for rectifying an AC power supplied from the power supply section 1, a plurality of input filters for smoothing the rectified powers, respectively. Each input filter includes a choke coil L1 and a capacitor C1, respectively. The apparatus also includes a plurality of inverter circuits 3 for respectively switching the smoothed powers provided from the input filters and for heating the heating plates.
The inverter circuit 3, for example, comprises switching transistors Q1 and Q2 for perforrning a switching operation according to switching control signals provided from a control section (not illustrated) to their bases, respectively, diodes D1 and D2 respectively connected in parallel to the transistors Q1 and Q2, and a resonance capacitor C2 for resonating with a working coil Lr1 in response to the switching operation of the transistors Q1 and Q2. The working coil Lr1 resonates with the capacitor C2, and heats the heating plate by induction heating.
According to the conventional induction cooking apparatus as constructed above, a plurality of inverter circuits are used to heat a plurality of heating plates. Specifically, n inverter circuits 3, 3-1, 3-2, . . . , 3-n are connected in parallel to the power supply section 1 to operate a plurality of working coils Lr1, Lr2, . . . Lrn.
The heating operation of the conventional induction cooking apparatus will now be explained in detail.
The AC power from the power supply section 1 is rectified by the rectifying section 2, and the rectified power is then applied to the inverter circuit 3 through the input filter composed of the choke coil L1 and the capacitor C1.
The transistors Q1 and Q2 in the inverter circuit 3 switch the current flowing through the working coil Lr1, causing food on the heating plate to be heated.
At this time, the transistors Q1 and Q2 receive the switching control signals from the control section (not illustrated) in a proper timing, and thus perform the switching operation with respect to the current flowing through the working coil.
Specifically, the transistor Q2 is turned on by the switching control signal initially provided from the control section to its base, while the transistor Q1 is turned off. Accordingly, the power supplied through the rectifying section 2 to the transistor Q2 flows through the working coil Lr1 to form a current loop, and this causes the working coil Lr1 and the capacitor C2 to resonate together.
Thereafter, the transistor Q1 is turned on by providing the switching control signal from the control section to its base, and thus the transistor Q2 is turned off. Accordingly, as the transistor Q1 is turned on, an inverse current caused by the current energy accumulated in the working coil Lr1 flows through the transistor Q1 to form a closed loop, and thus causes the current to flow through the working coil Lr1.
By repeating the switching operation as described above, the energy induced in the working coil Lr1 is transferred to the heating plate adjacent to the working coil Lr1, and heats the heating plate. At this time, the power is controlled by controlling the current flowing through the working coil Lr1 in accordance with the change of the switching frequency of the transistors Q1 and Q2.
As a result, the respective inverter circuits 3, 3-1, . . . , 3-n heat the respective heating plates through the respective working coils. The control of the output power of the respective inverter circuits is performed by frequency control as described above.
However, the conventional induction cooking apparatus has the drawback in that an accurate output control of the working coil cannot be achieved because of the interference noise caused by the operating frequency difference between the adjacent working coils. Further, because inverters, rectifiers, and input filters equal in number to the number of working coils are required, the overall circuitry is complicated, resulting in an increase in manufacturing cost.